When a document defined in a page description language (PDL) is output (e.g., to a printer), there are many use cases which benefit from the ability to define a watermark superimposed or composited with content of the document. For example, an author of a document may intend that a particular document be designated as a draft version of the document. The document may therefore bear an inscription designating a printed copy of the document as a draft version, in order that a printed copy not be confused with a finalised version of the document. In further examples, a document might feature a watermark indicating that the document is a representative sample only, and should not be issued to a commercial customer. A document may also be marked as being secret, and have a watermark reminding all persons who handle an output copy of the document to take special precautions to maintain secrecy of the content. As another example, a watermark may bear important safety or procedural instructions as to how depicted content should be used. In some cases, using a watermark provides a means to protect copyright or assert intellectual property ownership of the contents of a document.
A watermark may be as simple as a single word or short phrase in a single font. As another example, a watermark may incorporate a company logo or any other arbitrary graphical elements.
In some documents, content that is intended as a watermark is expressed in the same way (e.g., in the page description language) as other content on the page. In this case, it is not possible to identify which content was intended as a watermark, and which is normal document content. However, a page description language, such as the Portable Document Format (PDF) published by the International Organisation for Standardization as ISO 32000-1:2008, may provide a means of designating document content as being a “watermark annotation”. The page description language may ascribe a special semantic meaning to a particular item of document content that distinguishes that content as being an annotation that is a watermark. The particular item of the document content is therefore separate to normal content of a page within the document.
Annotations are items of content that are associated with a location on a particular page of a document, but are declared separately from the page content for that page. A computer program that interprets a document defined in such a page description language may then differentially process page content that is semantically marked as being a watermark annotation, such as controlling the appearance of a watermark annotation.
In some page description languages such as PDF, normal page content is typeset within an imageable page area defined by the document. In this instance, the position of each item of content is defined by a co-ordinate value. In contrast, for some other page description formats, content is dynamically repositioned to fill available space if, for example, dimensions of an output or display medium change. An imageable page area may be defined by specifying values for the height and width of the page. Objects that comprise the page content may then be placed upon the page using a co-ordinate system defined in terms of that imageable page area.
A page description language such as PDF may allow some types of annotation content (e.g., watermark annotations) to be placed upon an output medium using a placement value that is relative to actual dimensions of the output medium itself. In cases where a page description language allows for the placement of a watermark annotation to be defined with respect to actual dimensions of an output medium (e.g., a printed page, a display), a situation may arise in which a watermark annotation is placed somewhere on the output medium that does not overlap with document content that is typeset for a particular page size. FIGS. 1A, 1B and 1C show several examples in which a watermark annotation (e.g., 103, 107, 116, 117, 118, 119) does not overlap an imageable area defined for each page 102, 106 and 114, respectively. In such a situation, the part of the output medium bearing the watermark annotation (e.g., 103) may be simply cut off or otherwise not utilised. In effect, actual document content is no longer protected by the watermark (e.g., 103), and the original intention of the document author for employing the use of a watermark is not carried out. A user of the document may furthermore intentionally take advantage of the non-overlapping behaviour by setting up print parameters in order for the situations of FIGS. 1A, 1B and 1C to explicitly arise. In some cases the user may be motivated by a desire to circumvent the role of the watermark as a security mechanism or a means to otherwise limit the use of the document content.